An electrophotographic light-sensitive material may have various structures depending upon the characteristics required or an electrophotographic process to be employed.
Typical electrophotographic light-sensitive materials widely employed comprise a support having provided thereon at least one photoconductive layer and, if necessary, an insulating layer on the surface thereof. The electrophotographic light-sensitive material comprising a support and at least one photoconductive layer formed thereon is used for the image formation by an ordinary electrophotographic process including electrostatic charging, imagewise exposure, development, and, if desired, transfer.
Furthermore, a process using an electrophotographic light-sensitive material as an offset master plate precursor for direct plate making is widely practiced. In particular, a direct electrophotographic lithographic plate has recently become important as a system for printing On the order of from several hundreds to several thousands prints having a high image quality.
Under these circumstances, binder resins which are used for forming the photoconductive layer of an electrophotographic light-sensitive material are required to be excellent in the film-forming properties by themselves and the capability of dispersing photoconductive powder therein. Also, the photoconductive layer formed using the binder resin is required to have satisfactory adhesion to a base material or support. Further, the photoconductive layer formed by using the binder resin is required to have various excellent electrostatic characteristics such as high charging capacity, small dark decay, large light decay, and less fatigue due to prior light-exposure and also have excellent image forming properties, and the photoconductive layer stably maintains these electrostatic properties in spite of the fluctuation in humidity at the time of image formation.
Further, extensive studies have been made for lithographic printing plate precursors using an electrophotographic light-sensitive material, and for such a purpose, binder resins for a photoconductive layer which satisfy both the electrostatic characteristics as an electrophotographic light-sensitive material and printing properties as a printing plate precursor are required.
It has been found that the chemical structure of binder resin used in a photoconductive layer which contains at least an inorganic photoconductive substance, a spectral sensitizing dye and a binder resin has a great influence upon the. electrostatic characteristics as well as smoothness of the photoconductive layer. Among the electrostatic characteristics, dark charge retention rate (D.R.R.) and photosensitivity are particularly affected.
Techniques for improvements in smoothness and electrostatic characteristics of a photoconductive layer by using various types of low molecular weight resins having a component containing an acidic group are described, for example, in JP-A-63-217354 (the term "JP-A" as used herein means an "unexamined published Japanese Patent Application"), U.S. Pat. Nos. 4,968,572, 5,021,311, 5,134,051, 4,495,407, 5,063,130 and 5,089,368, EP-A-0389928 and EP-A-0432727.
Also, it is presumed that, even when the stoichiometeric defect of the inorganic photoconductive substance varies to some extents, a relatively stable interaction between the inorganic photoconductive substance, spectral sensitizing dye and resin may be maintained since the resin has a sufficient adsorptive domain by the function and mechanism of these various low molecular weight resins. In particular, when a graft type copolymer or an AB block copolymer is used, it is known that relatively stable performances can be obtained even when ambient conditions are varied.
Further, techniques for improving a mechanical strength of a photoconductive layer by using the above described low molecular weight resins containing an acidic group together with medium to high molecular weight resins are described, for example, in U.S. Pat. Nos. 4,871,638, 4,968,572, 4,952,475, 5,030,534, 5,009,975, 5,073,467, 5,077,166, 5,104,760 and 5,104,759, EP-A-0410324 and EP-A-0440226.